In certain applications such as the auxiliary power units used on aircraft, a gear box of the reduction drive type may be utilized. The reduction drive gear box typically requires oil for cooling and lubrication and a filter to maintain clean oil. In other words, the oil is typically passed through a replaceable filter element in a recirculation path of the cooling and lubrication system.
Normally, the oil will enter a filter chamber, pass through the filter element, and return to the gear box. To prevent a dirty oil filter element from "starving" the gear box of oil, a by-pass valve arrangement is provided. With such arrangements, the by-pass valve diverts oil around the dirty filter element back into the gear box.
In order to gain access to the filter element for replacement, it has usually been necessary to remove a retaining ring from a groove in the housing. Only then can the by-pass valve be removed so as to gain access to the filter element but, in many gear box applications, the retaining ring is located in a relatively inaccessible location. When this occurs, it is known to be very difficult to remove the retaining ring for replacement of the filter element during normal maintenance procedures.
In addition, a retaining ring is usually notched in the housing groove in a very secure manner. This means that it is not possible to remove the retaining ring and, thus, the by-pass valve and filter, without the use of tools. Of course, this only adds to the difficulty of performing normal maintenance procedure.
The present invention is directed to overcoming one or more of the foregoing problems and achieving one or more of the resulting objects.